posted 4 years ago
I highly recommend Art Ludwig's book and website for greywater systems.
At our off-grid school in the Indian Himalayas, we've been operating with extremely low-tech greywater system for some 20 or 25 years. It's equivalent of zone 5 or 6, and we've got 6 weeks of pond-hockey, if that gives you an idea of the climate. I've done the same at my house for the past 3 winters.
Burying pipes 3 feet underground is sufficient here to keep pipes from freezing. Then the issue is to make sure there's enough drop to keep water from pooling in the pipe, and enough drop-off to keep water from pooling and freezing and coming up to the level of the outlet (That turned out to be a problem at my house, where there was less slope).
Our school had a nice slope, so the outlet from the kitchen and bathroom drains could be buried 3 feet at least, and then come out to daylight at a canal that irrigates trees. The willow trees have been loving it and thriving for 25 years. We don't try to remove oil, reduce soap, or force our teenagers to abstain from the icky-gick "products" that they use. Letting the water straight out to daylight allows the topsoil organisms to deal with and digest everything. However, in summer, it can sometimes stink like greywater. In winter, it freezes over the surface, but our topography makes that a non problem. At my house, that was a problem when I had the outlet in a hollow covered with a piece of plywood. It froze up in layers and blocked the pipe late one winter; I had to remove the cover and break it with a shovel. The next year I left the cover off and made sure the hollow's outlet was well cleared, and then I think the occasional hot shower or bathtub draining kept it clear.
Ana Edey of Solviva fame on Martha's Vineyard off the coast of Massachusetts made an excellent underground contained toilet thingie that would be great for greywater if you want to put it all underground. Her toilet drains into a box in the ground full of wood chips and compost worms, with an insulated top. That in turn drains down to a perforated pipe laid in a trench of gravel protected with weed barrier cloth, that irrigates some pine trees. Pine trees don't have invasive roots, but many types of trees will aggressively get up into and block buried perforated pipes.
Works at a residential alternative high school in the Himalayas SECMOL.org . "Back home" is Cape Cod, E Coast USA.